This invention relates to an extrusion die for ceramic honeycomb structures, and more specifically to an extrusion die for ceramic honeycomb structures, each having a plurality of different walls thicknesses, such as catalyst carriers for the purification of engine exhaust gases, heat exchangers or rotors for superchargers.
The term "ceramic honeycomb structure" as used herein will hereinafter be in reference to a ceramic structure in which a plurality of through-holes are separated from each other by partition walls in the form of a honeycomb body.
There are known ceramic honeycomb structures which individually have a plurality of different wall thicknesses in each honeycomb body. Such honeycomb structures can improve the mechanical strength of peripheral edge portions thereof so that they may be used as catalyst carriers for the purification of automobile exhaust gases, whereby the outermost peripheral walls can be thicker (Japanese Patent Publication No. 28,850/79) and the partition walls can be thicker at outer peripheral parts thereof than inner parts thereof (Japanese Patent Publication No. 50,170/82). FIG. 1 illustrates a known extrusion dies for forming such a structure. As illustrated in FIG. 1, a die 1 provided with a mask 5 on a peripheral edge portion of discharge slots 2 corresponding to the cross-sectional outer shape of a ceramic honeycomb structure so as to unite extruded walls which correspond to the peripheral edge portion of the discharge slots. In addition, there has also been proposed, as shown in FIG. 2, a die 1 equipped with ceramic batch feed passageways 3, which are formed broader as the widths of their corresponding discharge slots 2 become greater.
Extrusion dies of such conventional structures may be employed for extruding honeycomb structures which have through-holes of geometrically-simple shapes such as triangular, square and hexagonal shapes and wall thicknesses which vary relatively little. However, when they were used to form honeycomb structures having wall thicknesses of at least two different types and defining through-holes having complex structures such as rotors for superchargers as depicted in FIG. 3, the extrusion speeds of extrudable ceramic batches is uneven and it is impossible to produce such honeycomb structures by known extrusion technique.